MONDAY, Feb. 1, 2016 (HealthDay News) -- Declining weight from middle-age years to late life may be a sign of impending dementia, a new Mayo Clinic study suggests.

People who lose weight over decades appear to have an increased risk for losing memory and thinking skills -- called mild cognitive impairment -- which can lead to dementia, including Alzheimer's disease. A loss of 11 pounds every 10 years may indicate as much as a 24 percent higher risk for loss of mental ability, researchers found.

"Unintended weight loss may be a signal to examine whether to increase efforts to engage in lifestyle measures that are beneficial to mental function," said lead researcher Dr. Rosebud Roberts, a professor of epidemiology and neurology at the Mayo Clinic in Rochester, Minn.

About 5 percent to 15 percent of adults who show early loss of mental ability progress to dementia, Roberts said.

For the study, Roberts and colleagues collected data on almost 1,900 men and women 70 and older who took part in the Mayo Clinic Study of Aging, which started in 2004. Their height and weight readings at midlife were taken from medical records.

During an average of over four years of follow-up, 524 people developed memory and thinking problems (mild cognitive impairment). These folks were more likely to be older or carrying the APOE e4 allele, a gene mutation associated with an increased risk of Alzheimer's disease.

Those who developed thinking and memory problems had a greater weight change per decade from midlife than those who remained mentally normal -- a loss of 4.4 pounds versus 2.6 pounds, the study said.

Keith Fargo, director of scientific programs and outreach at the Alzheimer's Association, pointed out that this study shows only an association between weight loss and a decline in mental ability, so "you can't really say anything about cause."

In addition, Fargo said the weight loss seen in the study may not be significant. Losing 11 pounds over 10 years works out to about a pound a year, which may be just normal weight fluctuation, he said.

In the study, weight loss occurred both in people who were obese in midlife and those who weren't obese, therefore the decline in weight "most likely results from as yet unidentified factors," Roberts said. The researchers couldn't determine whether the weight loss was intentional or unintentional, she said. However, the researchers did suspect that the weight loss was mostly unintentional, which was noted in the study.

"Symptoms such as depression or apathy that occur before dementia may also have an impact on diet. Changes in smell, which are associated with dementia, may also affect eating habits and lead to weight loss," she said.

Doctors should be on the lookout for patients who are losing weight for no apparent reason, Roberts said. "Unintended weight loss may help identify patients who may be declining mentally," she said.

The report was published Feb. 1 online in JAMA Neurology.

Fargo said he hopes this study doesn't dissuade anyone from losing weight. He said the best ways to keep your brain healthy are the same as keeping the rest of your body fit. "What's good for your heart is good for your brain," he said.

"It's important that people not take away from this study they go out and gain weight to protect their brain," Fargo said. "If you are overweight or obese you should do what you can to reduce that weight," he said.

Exercising, maintaining a normal weight, eating a healthy diet, not smoking and limiting alcohol are all things people can do to help stave off mental decline, he said.